1. Field of Invention
The present invention relates to a domestic appliance, and more particularly to an electric steamer and a control method thereof.
2. Description of Related Arts
In recent years, there has been a change in the eating habit for families in that people are changing from such conventional cooking methods as pan frying, deep frying and frying to steaming. The reason is that cooking food by steaming is much healthier than pan frying and deep frying. A conventional electric steamer usually utilizes mechanical temperature control and timer for controlling the cooking parameters of the electric steamer. Some conventional electric steamers utilize electrical temperature and timer control. There have been many developments in the control technology for electric steamers, and conventional electric steamers have been equipped with multi-functional control technology. A conventional steaming process comprises the following steps: first a user needs to add water into the electric steam. Second, the user needs to put a predetermined amount of food into the steamer. Third, the steamer is electrically connected to a power supply. Fourth, the user sets up all the steaming parameters for the electric steamers. Fifth, the user needs to start the electric steamer for steaming the food. When the steaming process is activated, the electric steamer is arranged to heat up the water stored therein for steaming the food for a predetermined period of time. When the steaming time lapses, the electric steamer is turned off automatically and the steaming process is completed.
Conventional steaming technology includes digital steaming control technology which is capable of using high power to heat up the water in the steamer during an initial period of the steaming and decreasing the power gradually after a predetermined period of steaming time has lapsed. This technology facilitate saving of energy by optimally controlling the power used for steaming. For example, a Chinese patent having a patent number of 200820092116.2 and a filing date of Feb. 1, 2008 discloses an electric steamer comprising a base, a water tank assembly supported by the base, a heating assembly, a ventilation arrangement, a food rack, a cover, a control circuitry, a circuit board, a control panel, and a partitioning member provided between the base and the food rack, wherein the heating assembly is disposed in the water tank assembly. Moreover, the water tank assembly is embodied as a flat heating element, and has a protective cover provided at a peripheral rim of the flat heating element.
Such conventional electric steamer has several disadvantages. First, the amount of steam produced by the conventional electric steamer is usually independent of the amount of food disposed therein. Thus, when a user put only a small amount of food in the electric steamer, the heat absorbed by the food is correspondingly small. However, the amount of steam generated by the electric steamer is not adjustable and remains largely constant. This makes the electric steamer generate an excessive amount of steam in this particular occasion. This excessive amount of steam is uncontrollably ejected from the electric steamer. Moreover, a lot of hot water may also come out from the cover which poses a danger to the user of the conventional electric steamer. The spilling of hot water or the ejection of the excessive steam makes the surrounding area of the electric steamer dirty, and generates a considerable waste of energy. On the other hand, when the user puts a lot of food into the electric steamer, since the amount of steam generated by the electric steamer is largely constant, the food may not be exposed to adequate account of steam and may not be fully cooked. Second, when the user wishes to add some more ingredients into the electric steamer, the conventional electric steamer may not be capable of promptly generating more steam so as to cope with the increased demand of food.